Whether intentionally or not, Yahoo briefly showcased some of its RSS search plans on Friday when Webloggers discovered and then posted screen shots of a Yahoo site for finding syndication feeds.

Yahoo Inc. executives previously have hinted at a possible search engine for blogs and feeds, but this week's sighting indicates that Yahoo is getting closer to releasing at least a test version of RSS search, search experts say.

It also could usher in competition from a major Web search player for startups such as Technorati Inc. and Feedster Inc., which concentrate on feed search.

A Yahoo spokesperson would neither confirm nor deny the appearance of Yahoo's test version of the RSS search site or provide details about the company's RSS search plans. At least three bloggers, though, were able to conduct and document a limited number of queries on a Yahoo RSS search site.

"We're always testing new services, but we have no comment on the screen shots," said Yahoo spokesperson Meagan Busath.

Steve Rubel, a vice president at public-relations agency CooperKatz & Co. Inc, first noted the Yahoo RSS search site on his Micro Persuasion blog. He came across the site when he noticed a new URL (test.rss.search.yahoo.com) appearing in his blog's visitor log, Rubel said.

Within hours of his post, the site was no longer available on the Web. The site included the familiar Yahoo Search query box but with two options for narrowing a search to "RSS" or to "RSS on My Yahoo."

Yahoo isn't the only large search engine exploring RSS and blog search. Ask Jeeves Inc. earlier this year bought Bloglines, a popular Web-based RSS aggregator, and said it planned to build blog-focused search.

As for Google Inc., the company has said little about RSS search other than that it is looking into it.

Both Yahoo and Microsoft Corp.'s MSN already provide syndication-feed search specifically for users of their respective personalized home-page services, but neither has released a broad RSS or blog search engine that indexes feeds.

Rubel said that Yahoo's momentary RSS-search site appeared to be an early test. He said that some features, such as options for adding feed into My Yahoo or viewing the XML of a feed, did not work for him.

But, he said, he expects Yahoo's entry into RSS search to raise the profile of feeds and blogs, which have been the earliest Web sites to embrace RSS.

"What Yahoo is doing is elevating the importance of searching blogs for the average consumer," Rubel said.

Danny Sullivan, the editor of Search Engine Watch and a longtime search watcher, also tried out the Yahoo site briefly before it disappeared. He said he has few doubts that Yahoo will eventually launch an RSS- or blog-focused search engine.

The bigger question will be how Yahoo defines which sites and feeds belong in the engine, since RSS feeds are now becoming popular far beyond blogs, and as the sites calling themselves "blogs" are extending beyond personal opinion journals, Sullivan said, while the same challenge faces the current breed of feed and blog search engines.

"If you're trying to get a measure of the blogosphere, you can't just depend on RSS, but you have to go through and cull the things that are [really are] blogs, and that will be harder and harder as more people have blogs," he said.

One benefit Yahoo and its bigger search rivals could bring to RSS and blog search is a greater focus on quality control in search results. Many of the current blog search engines face challenges in weeding out duplicate results or spam-oriented feeds, Sullivan said.